Topic 6: measure of association of risk/rate ratio

Question 1

Define exposure

Answer 1

• Independent variable
• An event/state/behavior = group of people is exposed to

Question 2

Define outcome

Answer 2

• Dependant variable
• Event/state/behavior = hypothesized to result from exposure to some variable

Question 3

Describe measures of association

Answer 3

• Assesses presence + magnitude of association between exposure + outcome
• How much change in outcome for given change in exposure

Question 4

Describe relative risk

Answer 4

• Comparison between 2 risks/incidences
• Is a measure of association = assess the probability of event/risk occurring in exposed group compared to same event occurring in unexposed/reference group
• Both exposure + outcome = categorical

Question 5

2 Types of relative risk

Answer 5

1) Risk ratio: ratio of 2 risks = cumulative
2) Rate ratio: ratio of 2 rates = incidence =AKA hazard ratio

Question 6

How to calculate risk ratio

Answer 6

Risk in exposed / Risk in unexposed
- Numerator = number of new cases over specific period exposed / number in total population at beginning of period exposed
- Denominator = number of new cases over specific period unexposed / number in total population at beginning of period unexposed

Question 7

How to calculate rate ratio

Answer 7

Rate in exposed / Rate in unexposed
- Numerator = number of new cases over specific period exposed / number in total person-time of follow-up in exposed
- Denominator = number of new cases over specific period unexposed / number in total person-time of follow-up in unexposed

Question 8

How to interpret results of relative risk

Answer 8

• > 1 = exposed have higher risk of outcome than unexposed = exposure is harmful
• <1 = exposed have lower risk of outcome than unexposed = exposure protective
• =1 = exposed have same risk as unexposed of outcome = exposure is not associated with outcome
• To find % = find difference from 1 then x 100
• Interpret as fold e.g. exposure have 4 fold higher risk than unexposed